SC4508 Buck or Buck-Boost(Inverting) Current Mode Controller POWER MANAGEMENT Description Features The SC4508 is a low voltage current mode switching regulator controller that drives a P-channel power MOSFET with programmable switching frequency. It can be configured in either buck or buck boost (inverting) converters. The converters can be operated from 2.7V to 15V input voltage range. The typical operating supply current is 3mA and a shutdown pin allows the user to turn the controller off reducing it to less than 200µA. The output voltage can adjusted by external resistor divider. The switching frequency is programmable up to 1.5MHz, allowing small inductor and capacitor values to minimize PCB space. The operating current level is programmable via an external sense resistor. Accessible reference voltage allows users to make output voltage as low as they want. Wide input voltage range 2.7V to 15V Programmable output voltage Programmable switching frequency up to 1.5MHz Buck or buck boost(inverting) configuration Current mode control with slope compensation Very low quiescent current in shutdown mode Accessible reference voltage MLPQ-12 package Applications Low power point of use converters Single or multiple output low power converters Positive and/or negative output voltage DSL cards Graphic cards I/O cards Negative bias supplies Typical Application Circuits Vin Vin VDD VDD VREF VREF FB+ SC4508 FB- CS FB+ OUT COMP SC4508 FB- OUT COMP SS/SHDN GND OSC SS/SHDN Revision: November 30, 2004 CS 1 GND OSC www.semtech.com SC4508 POWER MANAGEMENT Absolute Maximum Rating Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability. Parameter Symbol Maximum Units -0.3 to 16 V 3.2 V FB+, FB-, COMP, OSC to GND 5 V VREF Current 1 mA 250 mA VDD to GND SS/SHDN to GND OUT Source or Sink Thermal Resistance, Junction to Ambient θJA 48 °C/W Thermal Resistance, Junction to Case θJ C 3 °C/W Storage Temperature Range TSTG -60 to +150 °C Junction Temperature Range TJ -40 to +150 °C TPKG 260 °C Peak IR Reflow Temperature 10 - 40s Electrical Characteristics Unless specified: VDD = 2.7V to 15V , TA = TJ = -40°C to 125°C Parameter Test Conditions Min Typ Max Unit 15 V 500 µA Pow er Supply Input Voltage Range 2.7 Quiescent Current SHDN = low 200 Operating Current SHDN = high, No load 3 VDD rising 2.5 mA Undervoltage Lockout Start Threshold UVLO Hysteresis 2.55 100 V mV Oscillator Frequency Range Frequency 100 C T = 300pF 450 Charge Current 500 100 1500 KHz 550 KHz µA Error Amplifier Feedback Input Voltage 0.75 V Input Bias Current 100 nA Transconductance 5 mS 100 µA Output Source or Sink Current 2004 Semtech Corp. 50 2 www.semtech.com SC4508 POWER MANAGEMENT Electrical Characteristics Unless specified: VDD = 2.7V to 15V , TA = TJ = -40°C to 125°C Parameter Test Conditions Min Typ Max Unit PWM Comparator Delay to Output 50 ns VREF Reference Output Voltage 1.231 1.25 Output Current 1.269 V 1 mA Line Regulation VDD = 2.7 to 15V, IVREF = 1mA 4 mV Load Regulation VDD = 5V, IVREF = 0 to 1mA 4 mV Charge Current 20 µA Discharge Current 12 mA Soft Start/Shutdow n SHDN Logic Hight Voltage 2 V SHDN Logic Low Voltage 0.25 V 130 mV Current Limit Cycle by Cycle Threshold V D D = 5V 90 Shutdown Threshold Delay to Output 110 0.16 V 50 nS Output Gate Drive On-Resistance(H) VDD = 5V, ISOURCING = 250mA 20 Ohm Gate Drive On-Resistance(L) VDD = 5V, ISINK = 250mA 20 Ohm Rise Time COUT = 200pF 20 nS Fall Time COUT = 200pF 20 nS Note: (1) This device is ESD sensitive. Use of standard ESD handling precautions is required. 2004 Semtech Corp. 3 www.semtech.com SC4508 POWER MANAGEMENT Pin Configuration Ordering Information TOP VIEW VDD OSC COMP 12 11 10 OUT 1 9 FB+ CS 2 8 FB- SS/SHDN 3 7 PGND 4 5 6 VREF NC AGND DEVICE PACKAGE Temp. Range (TJ) SC4508IMLTRT(2) MLPQ-12(1) -40°C to 150°C Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. (MLPQ-12 4x4) Pin Descriptions Pin # Pin Name 1 OUT 2 CS 3 SS/SHDN 4 VREF 5 NC No connection. 6 AGND Analog ground. 7 PGND Power ground. 8 FB - Error amplifier inverting input. 9 FB + Error amplifier non-inverting input. 10 COMP 11 OSC Oscillator frequency set input. Connect a ceramic capacitor from OSC to AGND to set the internal oscillator frequency from 100KHz to 1.5MHz. Use equation to set the 100µA f= oscillator frequency. C is the capacitor from OSC to AGND. C • 0.65 12 VD D Supply voltage. Bypass a 1uF ceramic capacitor from VDD to PGND. - THERMAL PAD 2004 Semtech Corp. Pin Function Gate driver output for external P-MOSFET. OUT swings from VDD to PGND. Current sense input pin. Connect a current sense resistor between VDD and CS. Soft start pin. Connects an external capacitor between this pin and AGND. The ramp up time is defined by the capacitor. The device goes into shutdown when VSS/SHDN is pulled below 0.25V. 1.25V reference output. VREF can source up to 1mA. Bypass with a 0.1uF ceramic capacitor from VREF to AGND. Compensation pin for the internal transconductance error amplifier. Connect loop compensation network from COMP to AGND. Pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected internally. 4 www.semtech.com SC4508 POWER MANAGEMENT Block Diagram Marking Information Top View yyww = Date Code (Example: 0012) 2004 Semtech Corp. 5 www.semtech.com SC4508 POWER MANAGEMENT Application Information Inductor Selection The SC4508 is designed to control buck (step down) or buck-boost (inverting) converter with P-channel MOSFET as a switch using current mode, programmable switching frequency architecture. During steady state operation, the switch is turned on each cycle and turned off when the voltage across current sense resistor exceeds the voltage level at COMP pin set by voltage loop error amplifier. A fixed 0.5V artificial ramp is added internally to the sensed current signal for operations when dutycycle is larger than 50%. In over load or output shortage condition, if the sensed current signal reaching typical 120mV, the switch is turned off immediately in the same cycle. If the sensed current signal further increases to typical 160mV, not only the switch is turned off but also the soft start capacitor is discharged by a internal MOSFET to ground then charging back to threshold 250mV during which the switch is held off. With the “hiccup” mode over current protection, the thermal stress is reduced in the faulty conditions. A inductor is chosen based on the required output ripple current which is usually 20-30% of load current. The ripple current ∆I decreases with higher inductance and increases with higher input voltage VIN or output voltage VO. L= VIN − VO VO + VD ( ) for Buck fs • ∆IL VIN + VD L= VO + VD VIN ( ) for Buck-Boost fs • ∆IL VIN + VO + VD Specify the maximum inductor current larger than IL(pk) set by the current sense resistor RS to avoid the inductor core saturation. Input Capacitor CIN and Output Capacitor COUT Selection Current Sense and Current Limit Both input and output capacitors need to be sized to handle the ripple current safely. Buck converters have high ripple current in the input side while buck-boost converters have high ripple current in the both input and output capacitors. Therefore, the RMS value of the current must be less than the high frequency ripple rating of the capacitors. In continuous mode operation, The typical cycle-by-cycle current limit threshold in the current sense pin of the SC4508 is 120mV. The over current limit is assumed typical 120% of full load current. Then the current sense resistor can be calculated by the following equation: 120mV Rs = 120% • I (pk ) L IRMS _ INPUT _ CAP ≈ IO 1V −V VO ( VIN − VO ) VIN V +V for Buck IN O O D IL (pk) = IO + 2 f • L ( V + V ) for Buck s IN D IRMS _ CAP ≈ IO IL (pk ) = IO VIN + VO + VD VIN + VO + VD 1 VIN ( ) 2 fs • L VIN + VO + VD VO + VD for Buck-Boost input and output VIN capacitors. The C is selected for Buck converter is by required OUT output ripple voltage and converter loop stability. The output ripple is determined by: for Buck − Boost IO - full load current VO - output voltage VIN - input voltage VD - diode forward voltage drop fS - switching frequency L - inductor ∆VO ≈ ∆IL (ESR + 1 ) 8fs C OUT where f is converted switching frequency, C is output S OUT capacitance and ∆I is inductor ripple current. L 2004 Semtech Corp. 6 www.semtech.com SC4508 POWER MANAGEMENT Application Information (Cont.) LAYOUT GUIDELINES In Buck converter, the worst case input RMS ripple current occurs at 50% duty cycle, or at VIN = 2VOUT. Under this condition, the input capacitors RMS ripple current is about half of the load current. Careful attention to layout requirements are necessary for successful implementation of the SC4508 PWM controller. High switching currents are present in the application and their effect on ground plane voltage differentials must be understood and minimized. MOSFET Selection 1). The high power parts of the circuit should be laid out first. A ground plane should be used, the number and position of ground plane interruptions should be such as to not unnecessarily compromise ground plane integrity. Isolated or semi-isolated areas of the ground plane may be deliberately introduced to constrain ground currents to particular areas, for example, the input capacitor and output capacitor ground. The selection criteria for the power MOSFET is its operating junction temperature not exceeding the maximum junction temperature. Therefore, from a specified ambient temperature, the maximum junction to ambient temperature rise has to be determined, which is related to the MOSFET power dissipation or power loss. The power loss includes conduction loss and switching loss. The conduction loss is given by: PON = ( PON = ( 2). The loop formed by the Input Capacitor(s) (Cin), the MOSFET and the Schottky diode or inductor must be kept as small as possible. This loop contains all the high current, fast transition switching. Connections should be as wide and as short as possible to minimize loop inductance VO + VD 2 )IOR DS( ON) for Buck VIN + VD VIN + VO + VD VIN )( VO + VD )IO2 RDS( ON) for Buck-Boost 3). The connection between the junction of MOSFET, Schottky diode and the output inductor should be a wide trace or copper region. It should be as short as practical. Since this connection has fast voltage transitions, keeping this connection short will minimize EMI. Freewheeling Diode Selection The Schottky diode is recommended as freewheeling diode in the both Buck and Buck-Boost applications. The diode conducts during the off-time. The diode voltage and current ratings are selected based upon the peak reverse voltage, the peak current and average power dissipation. VD(REV ) = VIN , ID(PEAK ) = IO + 4) The Output Capacitor(s) (Cout) should be located as close to the load as possible, fast transient load currents are supplied by Cout only, and connections between Cout and the load must be short, wide copper areas to minimize inductance and resistance. ∆IL V − VO ,ID( AVG ) = IO IN for Buck 2 VIN + VD VD(REV ) = VIN + VO , ID(PEAK ) = IO ( VIN + VO + VD VIN )+ 5) A separate analog ground plane connects to the SC4508 AGND pin. All analog grounding path including decoupling capacitors, feedback resistors, compensation components, and current-limit setting resistors should be connected to this plane. ∆IL ,ID( AVG ) = IO 2 for Buck − Boost The most stressful condition for the diode occurs when the output is shorted. Under this condition, due to the VOUT = 0, the diode conducts at close to 100% duty cycle. Therefore, attention should be paid to the thermal condition when laying out a board. 2004 Semtech Corp. 7 www.semtech.com SC4508 POWER MANAGEMENT Evaluation Board Schematic, Buck 12V GND U1 SC4508 C4 1uF 12 VDD 3 C5 0.1uF SS/SHDN 11 C6 330pF f s=440KHz OSC 5 6 7 U1 CS OUT VREF NC FB+ AGND FB- PGND COMP R7 10K C3 1nF R1 0.09 R2 10 2 4 4 C2 47uF/16V TP1 1 C7 TP2 0.1uF 9 C1 47uF/16V 8 U2 FDFS2P102A 5 3 6 2 7 1 8 TP3 L1 10uH 6V/1A TP4 10 R4 20K C11 2.7nF C8 470uF/6.3V C9 470uF/6.3V GND C10 2nF R5 3.74K R6 TP5 TP6 TP7 1.24K TP8 Bill of Materials Item Quantity Reference 1 2 C1,C2 2 1 C3 1nF 3 1 C 4, 1uF 4 2 C5,C7 0.1uF 5 1 C6 330pF 6 2 C8,C9 7 1 C 10 2nF 8 1 C11 2.7nF 9 1 L1 10uH 10 1 R1 0.09 11 1 R2 10 12 1 R4 20K 13 1 R5 4.75K 14 1 R6 1.24K 15 1 R7 10K 16 1 U1 S C 4508 17 1 U2 F D F S 2P 102A 2004 Semtech Corp. Part 47uF/16V 470uF/6.3V 8 Manufacturer Sanyo P/N: 16TPB47M Sanyo P/N: 16TPB470M Semtech Corp. Fairchild P/N: FDFS2P102A www.semtech.com SC4508 POWER MANAGEMENT Evaluation Board Schematic, Buck-Boost TP9 12V GND U1 SC4508 C4 1uF 12 3 C5 0.1uF 11 C6 680pF 5 6 fs =2 5 0K H z 7 VDD SS/SHDN OSC U1 CS OUT VREF NC FB+ AGND FB- PGND COMP R7 10K C3 1nF TP10 2 R2 100 4 R8 249 C7 0.1uF 8 R9 1.0K 10 R4 20K D1 1N5819HW C2 47uF/16V TP1 U2 Si4831DY 4 5 1 9 C1 47uF/16V R1 0.1 C11 2.7nF 3 6 2 7 1 8 TP3 L1 33uH TP4 C10 100pF C8 47uF/16V C9 100uF/6.3V -5V/0.1A R5 6.04K GND R6 240 TP5 TP6 TP7 TP8 Bill of Materials Item Quantity Reference 1 3 C1,C2,C8 2 1 C3 1nF 3 1 C4 1uF 4 2 C 5, C 7 0.1uF 5 1 C6 680pF 6 1 C9 100uF/6.3V 7 1 C 10 100pF 8 1 C11 2.7nF 9 1 D6 1N5819HW 10 1 L1 3.3uH 11 1 R1 0.1 12 1 R2 100 13 1 R4 20K 14 1 R5 6.04K 15 2 R6, R8 249 16 1 R7 10K 17 1 R9 1.0K 19 1 U1 S C 4508 20 1 U2 S i 4831D Y 2004 Semtech Corp. Part 47uF/16V 9 Manufacturer Sanyo P/N: 16TPB47M Semtech Corp. Vishay www.semtech.com SC4508 POWER MANAGEMENT Outline Drawing - MLPQ-12, 4 x 4 A D DIM B PIN 1 INDICATOR (LASER MARK) A A1 A2 b D D1 E E1 e L N aaa bbb E A2 A DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .031 .040 .002 .000 (.008) .010 .012 .014 .153 .157 .161 .074 .085 .089 .153 .157 .161 .074 .085 .089 .031 BSC .018 .022 .026 12 .003 .004 1.00 0.80 0.05 0.00 (0.20) 0.25 0.30 0.35 3.90 4.00 4.10 1.90 2.15 2.25 3.90 4.00 4.10 1.90 2.15 2.25 0.80 BSC 0.45 0.55 0.65 12 0.08 0.10 SEATING PLANE aaa C C A1 D1 LxN E/2 E1 2 1 N bxN bbb e C A B D/2 NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. Land Pattern - MLPQ-12, 4 x 4 K DIM 2x (C) H 2x G Y X 2x Z C G H K P X Y Z DIMENSIONS INCHES MILLIMETERS (.148) .106 .091 .091 .031 .016 .041 .189 (3.75) 2.70 2.30 2.30 0.80 0.40 1.05 4.80 P NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804 2004 Semtech Corp. 10 www.semtech.com